1. Field of the Invention
The present invention generally relates to a spine formation device to form a spine of a bundle of folded sheets, a post-processing apparatus including the spine formation device, and a spine formation system including the spine formation device and an image forming apparatus, and a method of forming a spine of a booklet.
2. Discussion of the Background Art
Post-processing apparatuses to perform post processing of recording media, such as aligning, sorting, stapling, punching, and folding of sheets, are widely used and are often disposed downstream from an image forming apparatus to perform post-processing of the sheets output from the image forming apparatus. At present, post-processing apparatuses generally perform saddle-stitching along a centerline of sheets in addition to conventional edge-stitching along an edge portion of sheets.
However, when a bundle of sheets (hereinafter “booklet”) is saddle-stitched or saddle-stapled and then folded in two, its folded portion, that is, a portion around its spine, tends to bulge, degrading the overall appearance of the booklet. In addition, because the bulging spine makes the booklet thicker on the spine side and thinner on the opposite side, when the booklets are piled together with the bulging spines on the same side, the piled booklets tilt more as the number of the booklets increases. Consequently, the booklets might fall over when piled together.
By contrast, when the spine of the booklet is flattened, bulging of the booklet can be reduced, and accordingly multiple booklets can be piled together. This flattening is important for ease of storage and transport because it is difficult to stack booklets together if their spines bulge, making it difficult to store or carry them. With this reformation, a relatively large number of booklets can be piled together.
It is to be noted that the term “spine” used herein means not only the stitched side of the booklet but also portions of the front cover and the back cover continuous with the spine.
To improve the quality of the finished product, several approaches, described below, for shaping the folded portion of a bundle of saddle-stitched sheets have been proposed.
For example, in JP-2001-260564-A, the spine of the booklet is flattened using a pressing member configured to sandwich an end portion of the booklet adjacent to the spine and a spine-forming roller configured to roll in a longitudinal direction of the spine while contacting the spine of the booklet. The spine-forming roller moves at least once over the entire length of the spine of the booklet being fixed by the pressing member while applying to the spine a pressure sufficient to flatten the spine.
Although this approach can flatten the spine of the booklet to a certain extent, it is possible that the sheets might wrinkle and be torn around the spine or folded portion because the pressure roller applies localized pressure to the spine continuously. Further, it takes longer to flatten the spine because the pressure roller moves over the entire length of the spine of the booklet. Moreover, because only the bulging portion is pressed with the spine-forming roller in this approach, the booklet can wrinkle in a direction perpendicular to the longitudinal direction in which the spine extends, degrading its appearance. In addition, with larger sheet sizes, productivity decreases because it takes longer for the spine-forming roller to move over the entire length of the spine of the booklet.
Therefore, for example, in JP-2007-237562-A, the spine of the booklet is flattened using a spine pressing member (e.g., a spine pressing plate) pressed against the spine of the booklet, a sandwiching member that sandwiches the booklet from the front side and the back side, and a pressure member disposed downstream from the sandwiching member in a direction in which the bundle of folded sheets is transported. After the spine pressing plate is pressed against the spine of the booklet, the pressure member squeezes the spine from the side, that is, in the direction of the thickness of the booklet to reduce bulging of the spine.
Although this approach can reduce, in spine formation, wrinkles of and damage to the booklet caused by the first method described above, the processing time can be still relatively long because the sandwiching member and the pressure member are operated sequentially after the booklet is pressed against the spine pressing plate. In addition, the device is bulky because a motor is necessary to move the spine pressing plate in a reverse direction of the sheet conveyance direction. Further, a relatively large driving force is necessary because the pressing member squeezes the booklet in a relatively small area between the spine pressing plate and the sandwiching member while the folded portion of the booklet is pressed against the spine pressing plate, increasing the power consumption, which is not desirable.
In view of the foregoing, the inventors of the present invention recognize that there is a need to reduce bulging of booklets while reducing the processing time as well as damage to the booklet, which known approaches fail to do.